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Watershed assessment of portions of the Clark's Fork Yellowstone, Bighhorn [sic] Lake, and Shoshone subbasins, Montana and Wyoming

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Watershed assessment of portions of the Clark's Fork Yellowstone, Bighhorn [sic] Lake, and Shoshone subbasins, Montana and Wyoming


Published 2008
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"May 2008" - cover

Includes bibliographical references (p. 43-45)

This report summarizes results from a multi-scale ecological assessment of seven watersheds in the Clark?s Fork Yellowstone, Bighorn Lake, and Shoshone River subbasins in southern Montana and Wyoming. The area is unique in that it lies at the junction of three broad Level III ecoregions: the Wyoming Basin, the Middle Rockies, and the Northwestern Great Plains. It is bounded by the Beartooth Mountains on the west and the Pryor Mountains on the east. The Pryor Mountains and foothills are areas of especially high endemism for plants. The goal of the project was to provide landscape-level assessments of watershed health and integrity, as well as site-specific evaluations of wetland and aquatic condition within the 1,248,164 acre assessment area. This was accomplished using both broad-scale GIS analysis and field sampling. The value of watershed-level assessments lies in identifying areas where impacts are currently occurring or may occur, rather than merely documenting effects that have already occurred. By combining both site-level and watershed-level assessments, it is possible to select areas where management can make a substantial difference in future wetland and aquatic health. Our broad-scale GIS assessment examined underlying biological diversity, measured current conditions, and evaluated potential threats. Several key findings emerged from the GIS data analysis: ? Across the Montana portion of the assessment area, the BLM owns or manages approximately 217,000 acres, or 25% of the land. ? Across the assessment area as a whole, 50% of the land cover is shrubland, 32% is grassland, and 6% is forest. Wetlands make up less than 2% of the landcover. Pasture and cropland account for 9%. Both public and private grasslands and shrublands are used primarily for cattle grazing. ? In the Montana portion of the assessment area, there are currently 317 reservoirs ranging in size from 500 acres to less than 1 acre, 153 surface water diversions (dams, ditches, headgates, etc.) and 228 ground water diversions. Silver Tip Creek has the highest number of diversions, at 114, followed by Elbow Creek with 99. ? In terms of hydrology, topography, and vegetation communities, the Sage Creek 5th code HUC has the most complexity of the watersheds we evaluated, while the Silver Tip 5th code HUC has the lowest. ? All the watersheds received positive scores on a Composite Watershed Condition Index, which evaluates natural cover, stream corridor land use, riparian loss, and road disturbances. The Crooked Creek watershed had the highest score, while Silver Tip Creek and Bear Creek had the lowest. The Silver Tip watershed has extensive mining and agricultural impacts, while much of the Bear Creek watershed has lost riparian forests along tributary streams due to overgrazing, and its lower reaches have a heavy concentration of agriculture. ? The Bear Creek and Silver Tip Creek watersheds also had the highest scores on the Composite Threat Index, which assesses the potential risk from oil and gas extraction, riparian grazing, and residential development. The Bighorn River- Layout Creek watershed had the lowest score. We found in general, roads and road crossings are a disturbance in the assessment area. This was borne out by our field surveys, where we noted most roads follow valleys, and are often within eyesight of the stream. Road density is highest in the Sage Creek watershed and lowest in the Bighorn-Layout watershed, which also has the fewest road crossings per stream mile. Sage, Silver Tip and Bear Creek all have the highest number of road crossings per stream mile (0.63, 0.64, and 0.63 respectively). ? Our fine-scale rapid assessments focused on wetlands, ponds, springs and streams. We conducted Proper Functioning Condition (PFC) assessments at 73 sites and detailed aquatic surveys at thirteen sites. From the PFC surveys, we found most(51) sites were in proper functioning condition. Only 12 sites were found to be functioning at risk with a downward trend, and only four were non-functioning. Sites on BLM-managed land did not appear to be in any better or worse condition than sites under other management. ? When we compared the results of our surveys at BLM-managed sites where PFC surveys had been conducted in 2005, we found seven sites had degraded, 19 had improved, and 10 had stayed the same. In general, weeds and grazing were the most common source of impairment. ? In our aquatic surveys, we found significant environmental factors in this region (e.g. oil and gas fields, water diversions, improper grazing practices) appear to impair the biological health of some aquatic ecological systems, notably Silver Tip Creek, South Fork Bridger Creek, and Grove Creek. ? Three of the 13 visited lotic sites had good habitat quality, as ranked by at least one habitat assessment method. Five of the 13 sites were ranked slightly impaired and five moderately to severely impaired. ? High sediment loading was measured at both Silver Tip Creek sites, and in Grove Creek and South Fork Bridger Creek. The water conductivity values taken at both Silver Tip Creek sites and Clark?s Fork Yellowstone Site #1 were above the threshold (>3,000?s) for the water quality impairment level. ? Three native fish species, the longnose dace (Rhinichthys cataractae), longnose and white suckers (Catostomus catostomus and C. commersoni), and 112 macroinvertebrate taxa, were identified from the 13 aquatic survey sites. No Species of Concern were found

Carbon County, Montana

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Volume 2008
Publisher Helena, Mont. : Montana Natural Heritage Program
Pages 86
Language English
Call number 577.68
Book contributor Montana State Library
Contributor usage rights See terms
Collection MontanaStateLibrary; americana

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